Emmanuel Macron’s lead over Marine Le Pen has slipped six points since polls conducted just before the first round last Sunday.
However he is still as much as 20 points ahead.
According to pollster Harris Interactive, who correctly predicted the result of the first round with remarkable accuracy, Mr Macron now has a lead of 61% against Ms Le Pen’s 39%.
That compares to a poll carried out under the same conditions just before last Sunday’s vote which put Mr Macron at 67% and Ms Le Pen at 33%.
Importantly, the most recent Harris poll was conducted before Ms Le Pen announced an alliance with the defeated first round presidential candidate Nicolas Dupont-Aignan.
Mr Dupont-Aignan was sixth in the first round contest, securing 4.7% of the vote.
His party, Debout La France (Stand Up France), is an off-shoot of the conservative right. The alliance will be seen by some right-wing voters as attractive.
Ms Le Pen has said that Mr Dupont-Aignan would become her prime minister.
He once claimed he could never form an alliance with the far-right.
His policies are less extreme than hers, though he is deeply eurosceptic and a longstanding critic of the eurozone.
The newly formed duo released a joint statement on Saturday alongside a modified manifesto.
Within it, some of Ms Le Pen’s campaign pledges seem to have become more ambiguous.
There is no explicit mention of her promise to quit the single currency, and only a looser reference to ditching French membership of the EU.
Sections of the French media are claiming it represents an important u-turn designed to lure more voters.
Elderly right-wing voters had been particularly concerned about the pledge to quit the eurozone because of the effect it could have on their savings.
The two candidates have spent the weekend campaigning in different parts of the country.
Ms Le Pen was in the south of France on Sunday with a particular campaign message on the environment – a key issue for the now defeated far-left candidate Jean-Luc Melenchon.
It’s possible that far-right Ms Le Pen could, curiously, attract a proportion of far-left voters because despite their opposing views on immigration, Mr Melenchon and Ms Le Pen share some anti-establishment and anti-globalisation visions.
Ms Le Pen and her campaign team claim Mr Macron represents a bubble that will burst at the first national crisis.
He is, they say, representative of the globalist, borderless elite of politicians and financiers who have no interest in looking after real people.
“The country Mr Macron wants is no longer France; it’s a space, a wasteland, a trading room where there are only consumers and producers,” Ms Le Pen told a crowd of thousands of supporters in the southern city of Nice.
Conversely, Mr Macron’s team are casting Ms Le Pen as a dangerous xenophobe with a closed, narrow and nationalist vision.
They are attempting to persuade voters that Ms Le Pen’s “sanitisation” of her Front National party is an illusion.
They claim her attempt to broaden its image and policies beyond a longstanding hardline on immigration is simply a ploy to attract voters.
In the first round of voting last Sunday, Mr Macron secured 23.75% of the vote compared to Ms Le Pen’s 21.53%.
Given that half of voters didn’t choose either Ms Le Pen or Mr Macron, big question in this final week is which way will they all vote? Polling has revealed some surprising trends.
Both candidates will begin their final few days of campaigning with large rallies in the French capital later on Monday.
On Wednesday, the two will go head-to-head in a live televised debate.
The choice for voters is two starkly contrasting visions for France which will define the direction of the country and the continent.
The vote is on Sunday.